1. Field of Invention
The present invention relates generally to the field of inspection of ferrous tubular members, and more specifically to inspection of coiled tubing apparatus and methods of using the data from such inspections.
2. Related Art
Through the service life of a coiled tubing string (during its storage, transportation and workover operations), the mechanical integrity of the coiled tubing, such as tension capacity, fatigue life, burst or collapse pressure resistance, is constantly changing as a result of coiled tubing geometrical changes. For example, acidizing through coiled tubing could cause coiled tubing corrosion, while corrosion could lead to wall thickness loss or pitting on the surface of the coiled tubing; fracturing through coiled tubing could cause erosion on the coiled tubing surface, leading to significant wall thickness loss; high pressure coiled tubing operation could lead to ballooning (increase of outside diameter) and wall thinning; even during normal workover operation, the cross section of coiled tubing will gradually become oval and the length of coiled tubing may gradually grow. All these changes in coiled tubing geometry (wall thickness, diameter, shape) could compromise the mechanical integrity and the operability of the coiled tubing. For example, loss of wall thickness could lead to catastrophic failure of tubing parting, while a balloon section of coiled tubing could get stuck or crushed at the injector. Methods of using coiled tubing inspection data to improve coiled tubing operations are desired to address these needs.
Moreover, for many applications, it is not sufficient to make a single measurement or set of measurements at a single point along the coiled tubing. Tapered strings are known in the industry, for example, wherein the coiled tubing is manufactured with a steadily decreasing wall thickness from one end of the tubing to the other. It is also known in the industry to weld together lengths of coiled tubing. This can be done as an inexpensive approximation to a tapered string. It can also be done as a remedial activity as a way to remove a damaged section of tubing. Knowledge of the geometrical properties of the coil along the length of the tubing can also be used to better infer the friction as the coiled tubing is pushed into a wellbore. Knowledge of the change of such geometrical properties over time can be used to better estimate fatigue and useful life of the coiled tubing.
In addition, coiled tubing is known to experience gradual increase of permanent elongation through services. The amount of permanent elongation may not be uniform through the entire coiled tubing string. Hence, knowledge of simple diameter or wall thickness measurements relative to the length of coiled tubing may not be sufficient, especially for a tapered coiled tubing string. In many cases, knowledge of general geometry measurements (diameter, wall thickness, defects, etc, with a length reference) and its corresponding attributes in the original new (as manufactured) form are needed to better estimate the integrity of the coiled tubing.
For these reasons, it is clear that there is a need to make geometric measurements of the coiled tubing along the length of the coiled tubing and to store such measurements in a database that can be readily accessed. Moreover, there is a need to be able to manipulate such databases, for example to append two databases into one when two sections of coil are welded together, or to update a database if a section of tubing is removed. We refer to such a database as a geometric database. The database will typically be indexed by the distance along the coiled tubing but other indexing methods are known in the art.